Figure 2  Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) chart representing the search strategy. Total 281 articles were found eligible after applying the inclusion criteria. Original research articles reporting influenza virus types influenza A virus (IAV), influenza B virus (IBV), influenza C virus (ICV), and influenza D virus (IDV) in swine populations available until February 21, 2020 were downloaded from the PubMed and Google Scholar databases.